Multiple-plate radiation detectors



March 13, 1956 e. HERZOG 2,738,431

MULTIPLE-PLATE RADIATION DETECTORS Filed Feb. 14. 1952 74a 1 V I ZERO2001/.

ATTORNEY 1111111111111 I N V N TOR. I Z590 2001/, /000;/a, 6PHAPD HEPZOGI United States Patent 2,738,431 MULTIPLE-PLATE RADIATION DETECTORSGerhard Herzog, Houston, Te xi, assignor to The Texas Company, New York,N. Y., a corporation of Delaware ApplicationFeb'rua'ry I4, '1952,SerialN0. 271,544 8 Claims. (Cl. 25083.6)

This invention relates to improvements in Geiger- 15 Mueller radiationdetectors and in particular to the types thereof variously known asmultiple plate detectors, Hare detectors, and Texaco detectors. As isknown these de tectors have much higher efiiciencies for the detectionof penetrative radiation such asgamma rays than the original orproto-type Geiger-Mueller tubes. A brief review of why this is so willbe helpful in understanding the objects of the present invention and howthey are attained.

In proto-type Geiger-Mueller tubes the cathodes are cylindrical and areusually positioned, during operation, with their curved outer surfacesfacing broadside to the source of radiation. As a result of thisgeometry the great majority of the impinging penetrative photons neverget to 5 of the radiation which produced them, i. e., they will oftenmove off in directions having large components at right angles to theexposed surfaces of the cathode element. Therefore multiple platedetectors oflered a type of structure which results in an increase inthe percentage of interactions and at the same time permits a higherpercentage of be detected. This shortcoming, which is inherent in this 9type of tube, may come about in either or both of two ways: (1) because'many photonssimply fail to become involved in interactions within-thecathode, and therefore fail to produce the charged particles needed forionizing the gas filling of the tube if current pulses are to beproduced, and/or (2) because many of thecharged-particleby products ofthe interactions which do take place fail to escape from the cathodeinto the gas filled interior of the tube. It comes about primarily inthe first way because the cathode walls are so thin that the majority ofthe impinging photons of penetrative radiation go right through'theentire tube without having interactions. Nor does the presence of alarge volume of gas within the'tube improve matters to any substantialdegree since interactions'occur in substantial numbers only in densematerials, Thus, incidentally, it should be-borne in mind that the gas,which is so essential for the counting mechanism, i. e., for the gasamplification afforded by Townsend avalanches, is of substantially nosignificance in contributing to the total number of interactions. Itcomes about primarily in the second way because the cathode walls aresothick that a great many of such interactions as do take place will occurwithin them at greater distance from their interior surfaces than thepenetrative ranges of the charged-particles which are released asby-products of these interactions. In other words the charged-particleshave very limited capability for penetration as compared to the photonsof the initial radiation. From the foregoingit will beseen that there isno possible wall thicknessfor these tubes at which high de tectionefiiciencies will be achieved. All that can be hoped for is to avoidsuch extremely poor efficiencies that use of the tubes is impractical.

Multiple plate detectors haveprovided a great increase in detectionefliciency by the use of-stacked arrays of waferlike cathode elementswhose exposure to radiation is successive, if it is directed at theirsurfaces, and is deep, if it is directed at their edges. Thus a gammaray which impinges on an end of the stack will have repeatedopportunities to interact in thin elements from which the chargedparticle by-products can easily escape whereas one which enters an edgeof a cathode element or penetrates one-of its sides at a verysmallgrazing angle,'will have single excellent opportunity due to itscontinuous long path through the ionizing charged particles produced bythe interactions to escape into the gas.

To provide total edgewise areas of exposure of come sponding magnitudeto the broadside-areas afforded by the outer surfaces of the cylindricalcathodes of the proto-type Geiger-Mueller tubes, each of these tubesemployed a plurality of the wafer-like cathode elements arranged inslightly spaced-apart relationship to constitute a dense stacked array.As an overall result the multiple plate type detectors include, byvolume, much higher percentages of solid materials than was everpossible in the proto-type Geiger-Mueller tubes.

In addition to the occurrence of an interaction within the cathode, andof the escape of one or more ionizing charged particles from the pointof interaction into the gas filling of the tube, one more occurrence isnecessary to complete the detection of an intercepted photon ofradiation. It is that the charged particle(s) bring about a Townsendavalanche. To do this, it (or they) must ionize one or more atoms of thegas, i. e., produce secondary electrons, in a region within the tubeWhere a sufiicient accelerating gradient exists to start an avalanche ofionization. In proto-type Geiger-Mueller tubes this last requirement ismet almost automatically, in most cases, because all parts of theinterior surfaces of their cathodes are directly exposed to theircentrally located anodes. Therefore any negative charged particle whichescapesinto the interior of the tube and/ or any secondary electronwhichit produces by ionization has a very great likelihood of beingaccelerated toward the anode. To meet this requirement in multiple platedetectors, arrangements have been devised which are intended to affordunimpeded discharge paths to an anode from all regions, adjacent thesurfaces of the cathode elements, into which charged particles arelikely to escape. For example in many of these arrangements each of oneor more fine wire anodes extends in perpendicular, rather than parallel,relationship to the surfaces of the cathode elements, such as through arow of aligned holes formed respectively therein, the elements beingpositioned in alignment and adjacent to each other, though slightlyspaced apart, to make .this possible. Thus both surfaces of each elementcan see exposed portions of an anode along straight lines which areunobstructed by any part of any other cathode element. A simple exampleof such an arrangement is one in which each of the cathode elements is acircular disc having a small central aperture; the discs are arrangedwith their perimeters and apertures in alignment and their surfaces in aparallel spaced relationship; and a single fine wire anode extendsthrough the 0 f center of the aligned row of apertures.

Thus multiple plate detectors met two urgent needs: l) provision inthedetector head of greater amounts of dense material disposed in themost probable paths of the pene- .trative radiation to be detected';and(2) provision of a geometry affording a high-escape incidence of thechargedparticle by-products of interactions and open paths which do notphysically obstruct collection of the particles by the anode(s) despitethe large amounts of material comp1'isedin the cathode and thecomplex-arrangement thereof.

7 However these complex arrangements have the disadvantage that theyhave interfered with the electrical operationof the tube in such a waythat it is often difiicult to achieve a high percentage of actualcollection of the chargedparticle by-products and/or their secondariesby the anode(s) of the tube despite the open paths.

The difficulty arises from the fact that no interelement spacing is evertotally satisfactory. If very small spacings are used, c. g., with aview to increasing the number of cathode elements containable within agiven detector and thereby increase the incidence of interactions, thenthe electron-collecting field of the anode(s) is not able to penetratedeeply enough into the inter-element spacings to draw out most of theescaped charged particles and/ or the secondary electrons which theyproduce in the gas. Because of this many of these particles will not beable to start Townsend avalanches and the interactions which producedthese particles will go uncounted. If, on the other hand, large spacingsare used, c. g., to increase the efiiciency of the device for collectingescaped charge particles and/or the secondaries which they produce, thenthe incidence of interactions will be reduced.

Moreover, while it might seem that the collection of charged particlesin a detector which has excessively close spacings between its cathodeelements might easily be increased by increasing the anode-to-cathodepotential, this is not available as a satisfactory practical expedient.One reason for this is that certain anode potentials should not beexceeded if one is to obtain certain kinds of operation, e. g.,operation on the plateau or proportional counting. Another reason is thepossibility of cold emission from the edges of the cathode elementswhich face toward the anode(s) if an excessive anode-to-cathodepotential is used.

Similarly, while the collection of charged particles might be increasedby increasing the number of anode wires which pass through the stack ofcathode elements (see Figs. 3, 4, 5, 7 or 8 of U. S. Patent 2,397,071),it should be borne in mind that each time that a hole is made in acathode element it reduces the total amount of dense material comprisedtherein and thereby reduces the probable incidence of interactions.

Accordingly it is an object of the present invention to provideimprovements in Geiger-Mueller radiation detectors of the kind describedabove whereby one may use unusually small spacings between adjacentcathode elements and yet attain unexpectedly high efliciency incollecting the charged-particle by-products of interactions and/ or thesecondary electrons produced thereby.

In general these objects are attained by including in the detector meanswhich are effective independently of the anode(s) to provide inregion(s) into which charged particles are likely to escape and in whichtheir secondaries are likely to be produced, stronger collecting fieldsthan those which normally would be provided therein as a result of thepotential applied between the cathode and the fine-wire anode(s). As isknown there is a very great concentration of the available field about aGeiger- Mueller anode. Because of this the field gradients which existnear to portions of the cathode structure are relatively very low.According to embodiments of the present invention, which are shownherein by way of example, increased electron collecting fields areestablished in the regions in question by forcing direct currentsthrough or along the surfaces of the cathode elements radially outwardfrom the edges of their apertures to produce gradients which extendalong and between the electrodes as far as desired, whereby escapedcharged particles and/or their secondaries are forcibly drawn from theseregions and projected into the field(s) of the anode(s) wherein theyreceive their final acceleration for producing Townsend avalanches.

In the drawing:

Fig. 1 represents a longitudinal section through a multipie-plateGeiger-Mueller. detector embodying improvement features of the presentinvention;

Figs. 2-4 represent very much enlarged cross sectional views offragmentary portions of types of cathode elements which are suitable foruse in the detectors shown herein;

Fig. 5 is a fragmentary partially-sectioned view of another embodimentof the present invention; and

Figs. 6 and 7 represent plots showing qualitatively the difference inthe configurations of the fields which exist between the cathodeelements of prior art multiple-plate detectors and those of the presentinvention.

The detector 10 shown in Fig. 1 comprises a plurality of cathodeelements 11 positioned in parallel spaced relationship and having acentrally positioned row of aligned apertures 12 through which extends afine wire anode 13. This arrangement of the structure of the detector 10is in accordance with the prior art of so-called multipleplatedetectors.

The thicknesses and proportions of the various elements which appear inthe drawing and the spacings between them have been chosen forsimplicity and clarity and are not intended necessarily to berepresentative of actual dimensions. Likewise no attempt has been madein Fig. 1 to show cross sectional details of the cathode elements 11since this is not feasible in the small space available.

With regard to proportions which are suitable for the presentlydisclosed detector 10 the following is noted. According to the prior artthe spacings between cathode plates of any given diameter cant bereduced beyond a certain point without adversely effecting thecollection of charged particles as explained above. For example, theconclusion has been empirically reached that cathode elements having twoinch diameters should not be spaced any less than W of an inch apart.However by using means as proposed herein to set up strong electronaccelerating fields in the interelement spacings, independently of theanode(s) fields the spacings of the cathode plates can be madeconsiderably smaller than was ever previously possible.

The active electrode parts of the detector 10, e. g., its cathodeelements 11 and its anode 13 are mounted within an hermetically sealedenvelope comprising a rather thinwalled cylinder 14 and end closures 15and 16 joined together, for example by R. F. Welding, soldering in ahydrogen atmosphere, brazing or the like, in the assembled relationshipshown in Fig. 1. The diameter of the cathode elements 11 is such theyfit snugly within the cylinder 14. They may be supported therein in avariety of suitable ways such as by being press fitted thereinto and/orspot welded. A ring-shaped or annular spacer 17 may also be press fittedinto the cylinder 14 between each pair of cathode elements 11 toruggedize the structure; to maintain proper spacing between theelements; and to perform an electronoptical function which is to befurther described below. The anode 13 is supported under tension betweena pair of insulating, e. g., glass or ceramic beads 18 which are sealedinto centrally located openings Within the end closures 15 and 16.

According to the present invention electric fields for thepre-acceleration toward the anode(s) of negative charged particles whichescape into or are produced within the inter-cathode-element spacingsare provided for by forcing currents through, or along the surfaces of,the cathode elements from the edges of their apertures 12 radiallyoutward to their circular perimeters. To this end their perimeters areconductively connected to the metallic inter surface of the cylinder 14which therefore may serve as a terminal to which the negative pole of acurrent source may be connected, while the inner edges of theirapertures 12 should preferably be sutficiently conductive so that anypoints thereof can serve as terminals to which the positive pole can beconnected to cause substantially equal currents to be forced radiallyoutward toward the perimeter of the element over equivalent segmentsthereof. Any suitable means may be employed for causing the inner edgesto be appropriately conductive. For example conductive coatof conductiveor partially Conductive material.

ings, like the coatings 20 shown in Figs. 2-4 maybe used, these beingapplied by applying a liquid or paste, e. g., aquadag solution orsilver 1. aste, or by sputtering on a material such as gold While theflat sides of the elements are appropriately covered with masks ortemplates. A lead 19 is utilized to provide a common and externalterminal for connection of the inner edges 'of all of the apertures 12to the positive pole of a current source. It comprises one portion whichis connected in parallel to the inner edges of all of the apertures andanother which extends through the end closure 16 via an insulating bead21 to provide an external terminal pin. In the simplest type ofembodiment the cathode elements 11 may be made of an homogeneousmaterial having such a value of resistivity for a given solid volumethat for the particular dimensions of the cathode elements a voltagedrop adequate to provide the desired accelerating fields will bemaintained along all radii between the inner edges of their apertures12' and their outer perimeters for the expenditure of currents ofpractical magnitudes, i. e., of relatively small currents; I Because ofa beaming electron o tical etfect'which will occur between the cathodeelements 11 during the operation of the detector 10, the high potentialportions of its cathode elements will draw little or no current from theadjacent ionized gaseous filling, G, even when the detector might becounting at a very high rate. For this reason a current source 22 whichis connected between the inner and outer edges of the cathode elements11 does not have to be capable of providingmuch'power. Accordingly theresistivity of the cathode elements as measured between the inner edgesof their apertures 12 and their outer perimeters may he made extremelyhigh whereby it will itself serve 'to limit the amount of current drawnfrom the source of current 22 and will at the same time cause most ofthe voltage drop in the current loop to occur usefully along the surfaceof the cathode elements.

Figs. 24 represent structures for the cathode elements 11 which make itpossible for them to have the desired high resistance between theirinner and outer edges and also to have other desirable characteristicsas explained below. The simplest of these is that of Fig. 4. In thisembodiment a cathode element 11a comprises an insulating core 23carrying directly on all of its top, bottom and edge surfaces anextremely thin film or coating 24 coating 24, for example, may be a verythin, such as monomolecular, layer of tungsten or other metal which hasbeen evaporated onto the core, and in this way may readily be formedwith desired high values of resistance. As is shown in Fig. 4 the inneredge of the aperture 12 of the element 11a carries a coating 20 forcausing the edge to be more highly conductive than'the other surfaces ofthe element whereby the entire inner edge will be at the same potentialeven if the current source is connected to it at a single point as forexample by the lead 19.

An objection to making the cathode elements of a homogeneous resistiveor insulating material, such as, on the one hand, the sort of materialused for commercial carbon resistors for the elements 11, or, on theother, of a glass or ceramic material, for the insulating cores 23, isthat the principal ingredients of most suitable kinds of such substancesare usually low atomic number elements. However, as is known, suchelements are not as capable of absorbing penetrative radiation as highatomic number elements and for this reason their use is not to bepreferred for the cathodes of Geiger-Mueller detectors.

The embodiments shown in Figs. 2 and 3 have been devised to providecathode elements which, in addition to having high electricalresistance, also comprise large percentages of high atomic numberelements. To this end the element 11b shown inFig. 2 comprises as a core'25, some preferred type of cathode element formed of a high atomicnumber element, such as tantalum, but further includes an intermediateinsulating coating 26 to prevent the core from short circuiting thecoating 24. The insulating coating 26 may be of any suitable kind suchas a coating of aluminum oxide applied over the core 26 as an oxide or,if preferred, applied by evaporating or sputtering a layer of metallicaluminium onto it and then oxidizing all of the exposed surface(s) ofthe layer.

The coatings 24 and 20 of the element ll'b may be applied over theassembly comprising the core 25 and the insulating coating 26 in muchthe same way that as they are applied over the homogeneous core 23 ofthe element 11a and their functions in this embodiment are similar tothose of that of Fig. 4.

The embodiment of Fig. 3 utilizes a special core 27 which comprises highatomic number particles sintered together in an insulating binder sothat there will be no unbroken conductive paths from one point toanother either through the core or along its surfaces, even if theparticles are individually conductive, as they will be if they arefilings of a metal such as tantalum. Suitable techniques for making thespecial cores 27 are available in such arts as that related to themanufacture of highpermeability di-electric ferrite cores for highfrequency inductors, transformers, and the like. Because of the specialconstruction used for the core 27 the coating 24 may be applied directlyover it as shown in Fig. 3, i. e., without the use of an intermediateinsulating coating. In this embodiment, as in the others, the insideedge of the aperture 12 carries a coating 20 to serve a useful purposewhich has already been explained.

Fig. 6 represents how a part of the anode-to-cathode field in a priorart multiple plate detector fringes into the space between its cathodeelements. Since most of the field is concentrated about the fine wireGeiger-Mueller anode, equi-potential surfaces which are approximatelymidway between the anode and inside edges of the apertures 12 may havevalues which are but small fractions of the anode potential, for examplevalues in the neighborhood of 200 volts for an applied anode potentialof 1,000 volts. Due to this nonlinear falling off of the field gradientsat positions successfully farther removed from the anode toward thecathode array none of the equi-potential surfaces which are near enoughto the array to protrude or fringe into its interelement spaces willhave very great magnitudes. Thus Fig. 6 shows that while oneequipotential surface, which is represented as having a potential ofonly 44 volts, does bulge toward the interelement space shown therein,it actually does not extend into it. One surface which is shown tofringe about one fifth of the way into the interelement space providesno more than a 6 volt gradient over the other four fifths of the way,and this, of course, is not a very high voltage for controlling suchparticles as photo-electrons, Compton electrons, and the sort ofsecondary electrons which they will produce in ionizing the gaseousfilling G. Moreover this six volt gradient is also extremely nonlinearso that most of it is effective in a practical sense but for a verysmall fraction of the above-mentioned other four-fifths of the way. As aresult many negative charged particles which will escape from thecathode elements into a portion of each interelement space near theperiphery of the detector may never escape out of the cathode array toregions where they can be accelerated toward the anode. Of course, suchparticles may have initial velocities of their own in such directionsthat they will escape from the cathode array without anypm-acceleration," but this will be largely a matter of chance.

Fig. 7 shows how this situation is improved by arrangements such asthose proposed herein. For one thing the pronounced nonlinearity of thefield between the Geiger-Mueller anode and cathode has no significantinfluence on the magnitudes and the gradients of the fields which areestablished within'the cathode array, and are determined in the main bythe potential difference which is maintained between the inner and outeredges of the cathode elements and the linearity of the inter-edgeresistances of the cathode elements. Of course,this resistance will tendto be nonlinear because in each cathode element the volume of materialfor a given radiallymeasured' increment is progressively greater atpoints which are located successively nearer to its perimeter. Thisnonlinearity however is far less pronounced than that of the fielddistribution represented in Fig. and moreover it can be easilycompensated for by forming the elements to be thinner and/ or morehighly resistive in regions successively nearer to their perimeters.

Fig. 7 shows how one may maintain a voltage difference of about 200volts between the inner and outer edges of a cathode element so thatstrong [ire-accelerating fields are provided in all regions within thecathode array into which the charged-particle ivy-products ofinteractions are likely to escape. Of course it is desirable for thesenegative particles, and/or the secondary electrons which they produce,to be beamed away from the surfaces of the plates so that they will notbe recaptured thereon. To a certain extent some beaming action will beinherent due to the fact that the pre-accelerating fields within thecathode array will include a component which is contributed by the fieldof the anode and this component will have a configuration having anelectron optical effect which is suitable for the purpose at hand. Tofurther form the equi-potential surfaces with configurations suitablefor such electron optical efiects, the ring-shaped spacers 17 shownherein are formed with convex annular grooves facing inwardly in themanner shown in Fig. 1. Thus, since both the zero equi-potential surfaceand the components which are contributed by the field of the anode willbe convex toward the anode the resultant surfaces will be similarlyconvex.

In a detector which is modified according to the present invention itmay be necessary to use a slightly different anode potential than wouldbe employed if the detector were not modified as shown herein to obtaincertain desired kinds of operation, for example operation on theplateau. For this reason the potential source 30 shown in Fig. l isrepresented as providing an anode potential of: about 1,200 voltsinstead of, as is commonly the case, one about 1,000 volts.

If the amount of pre-acceleration employed within the array raises thenegative particles to energy levels higher than the ionization potentialof the gaseous filling of the detector, some electron multiplicationwill occur even before these particles pass out of the cathode array andinto the direct influence of the anode field. As is known the ionizingpotential which is essential for providing electron multiplication toproduce a Townsend avalanche in prior art Geiger-Mueller detectors mustbe effectively eliminated immediately after the generation of an outputpulse so that a detector can recover and therefore be ready for newcounts. Otherwise the potential will also eventually accelerate theheavy positive ions back onto the cathode thereby producing secondaryelectrons and sustaining a continuous discharge. it is to avoid thisthat large quenching resistor 31 is usually employed in series with acathode-to-anodc energ zing source. During a pulse it drops the appliedpotential to such a low value that the weak fields that remain withinthe detector cannot sufiicicntly accelerate the positive ions and freeelectrons to prolong the avalanches which produced these particles.Therefore all further ionization ceases and these residual particles arefree either to diffuse thermally to the side walls, and similar interiorsurfaces of the tube where they can be absorbed in recombinations, or toget there by a combination of thermal ambi-polar diffusion and theaiding effect of being swept (in opposite direc-.

tions and at lower than ionizing velocities) by and through these weakfields. Accordingly it may also be necessary at the end of a pulse toterminate the electron multiplication which is produced bypre-acceleration within the cathode array so that it will not interferewith successful quenching of the tube. To this end an electronic switch32 may be employed to disconnect the current source 22 from the cathodearray during the terminal portion of each generated out-put pulse andthe switch 32 may have its input connected to the anode 13 of the tube10 so that the pulses generated in the detector can be used to actuateit. If preferred the switch may be utilized to reduce the currentprovided by the source 22, rather than to cut it off entirely, so as toleave reduced sweeping fields Within the cathode array which may assistin recovery even though they are too weak to produce or sustainionization.

In order to provide very flexible control of pre-acceleration, theoutput voltage of current source should be adjustable in magnitude, asrepresented by the arrow associated with the source 22 in Fig. l, andreversible in polarity, as by actuation of the double pole double throwswitch 33 which also appears in this figure.

By reversing the polarity of the source 22 fields will be producedwithin the cathode array which will oppose the field of the anode ratherthan to aid it, i. e., which will actually urge and/or acceleratenegative particles away from, rather than toward, the anode(s). Thepossibility of thus operating the detector 10 can be very useful forcertain kinds of detection in which, as is well known, it may beadvantageous to reduce the efiiciency of the detector.

Fig. 5 shows a portion of a multiple-anode type of multiple platedetector. As is known this type of multiple plate detector employscathode elements, such as the elements 11d of Fig. 5, each of which hasa plurality of apertures (12) rather than a single, e. g., central, one,the detector being arranged so that there are as many fine wire anodespassing through the cathode array as the number of apertures in eachelement. This type of construction is preferably used for detectorswhich need to be relatively small in length and large in diameter ratherthan the converse. Thus a thin-walled cylinder 14a comprised in theenvelope of this type of multiple plate detector will be like thecylinder 14 of the Fig. 1 embodiment except that it will be of largerdiameter, and similar correspondence will exist between the annularspacers 17a of this detector and the spacers 17 of that of Fig. 1.

In this embodiment Y-shaped conductive electrode coatings 34 are appliedto the surfaces of each of the cathode elements 11d so that, for reasonswhich will be readily understood by those familiar with the art, thepre-accelerating fields will be substantially as intense ininter-element regions near the center of the cathode array as ininterelement regions near its perimeters.

Obviously many modifications and variations of the invention, ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

Iclaim:

l. A detector of penetrative radiation comprising a cathode arrayincluding a plurality of wafer-like elements stacked together with theirsurfaces in spaced-apart and coextensive relationship; an anodeinsulatingly supported within the array to receive therewithin chargedparticles escaping from a plurality of said elements, terminal meansconnectable' to an external high voltage source for establishing anelectric field between said array and said anode; and means responsiveupon connection of the array to another source of electrical energy toprovide within the array and substantially throughout the spaces betweensaid wafer-like elements electric fields supplementing saidfirstmentioned field in controllingthe movement of negative chargedparticles along said spaces and toward said anode.

2. A radiation detector comprising a cathode array including a pluralityof electrically connected wafer-like cathode elements stacked togetherwith their surfaces in spaced-apart and co-extensive relationship; ananode insulatingly supported within the array to receive therewithincharged particles escaping from a plurality of said elements, saidelements comprising resistive material whereby they are adapted to offeralong surfaces thereof which face each other significant conduction andsubstantial resistance to the flow of electrical current in directionsaligned with the anode; and terminals for connecting said elements to apotential source for forcing electrical currents along said surfacesthereof in said directions.

3. A radiation detector comprising a cathode array including a pluralityof apertured wafer-like electrically connected cathode elements stackedtogether with their surfaces in spaced-apart, and co-extensiverelationship and their apertures in alignment, an anode supportedcentrally within a row of said apertures of the array to receivetherewithin charged particles escaping from a plurality of saidelements, said elements being comprised of resistive material wherebythey are adapted to offer along surfaces thereof which face each othersignificant conduction and substantial resistance to the flow ofelectrical current in substantially radial directions with respect tothe edges of the apertures; and terminals for connecting said elementsto a potential source for forcing electrical currents along saidsurfaces in said directions.

4. A radiation detector comprising a cathode array including a pluralityof electrically connected wafer-like cathode elements stacked togetherwith their surfaces in spaced-apart and co-extensive relationship; ananode insulatingly supported Within the array to receive therewithincharged particles escaping from a plurality of said elements, each ofsaid elements comprising an insulating core and areas of the corescorresponding to said surface being coated with thin films of resistivematerial whereby said elements are adapted to offer along surfacesthereof which face each other significant conduction and substantialresistance to the flow of electrical current in directions aligned withthe anode; and terminals for connecting said elements to a potentialsource for forcing electrical currents along said surface thereof insaid directions.

5. A detector as in claim 4 in which said insulating core comprises highatomic number particles which may be individually conductive but areelectrically isolated by being bound together in an insulating matrix.

6. A radiation detector comprising a cathode array including a pluralityof electrically connected wafer-like cathode elements stacked togetherwith their surfaces in spaced-apart and co-extensive relationship; ananode insulatingly supported within the array to. receive therebetweencharged particles escaping from a plurality of said elements, each ofsaid elements comprising a core which includes a high atomic numberelement, areas of the cores which correspond to said surfaces beingcoated with insulating material, the insulating coatings being coatedwith thin films of resistive material, whereby said elements are adaptedto offer along surfaces thereof which face each other significantconduction and substantial resistance to the flow of electrical currentin directions aligned with the anode; and terminals for connecting saidelements to a potential source for forcing electrical currents alongsaid surfaces thereof in said directions.

- 1 7. In a radiation detecting device comprising a plurality of platesdisposedin separated relation and connected together electrically toform a cathode member, each plate being provided with at least one holeand the holes in the plates being disposed in alignment, an anode membercomprising a wire extending through said aligned holes and insulatedfrom said cathode plates, the improvement wherein said cathode platesare comprised of resistive material and adapted and arranged to have anelectric potential applied thereto between separate locations located atdifferent distances from the anode member, whereby an electric field maybe developed in the space between the adjacent cathode plates in radialdirections with respect to the anode member.

8. A radiation detector of the Geiger counter type comprising aplurality of plates arranged in a substantially parallel bank andconnected together electrically to form a cathode, the plates beingseparated slightly to form spaces therebetween, each of said platesbeing provided with at least one hole therein, the respective holesbeing disposed in a line extending transversely through said bank, ananode wire extending through said holes, said platesbeing comprised ofresistive material, and means for applying an electric potential betweentwo locations on said cathode member at diiferent distances from saidanode wire, thereby to produce a potential gradient along said member inradial directions with respect to said anode wire.

References Cited in the file of this patent UNITED STATES PATENTS2,440,511 Hare Apr. 27, 1948 2,480,808 Fearon Aug. 30, 1949 2,499,489Goldstein et a1. Mar. 7, 1950 2,519,007 Wilson Aug. 15, 1950 2,606,295Scherbatskoy Aug. 5, 1952

1. A DETECTOR OF PENETRATIVE RADIATION COMPRISING A CATHODE ARRAYINCLUDING A PLURALITY OF WAFER-LIKE ELEMENTS STACKED TOGETHER WITH THEIRSURFACES IN SPACED-APART AND COEXTENSIVE RELATIONSHIP; AN ANODEINSULATINGLY SUPPORTED WITHIN THE ARRAY TO RECEIVE THEREWITHIN CHARGEDPARTICLES ESCAPING FROM A PLURALITY OF SAID ELEMENTS, TERMINAL MEANSCONNECTABLE TO AN EXTERNAL HIGH VOLTAGE SOURCE FOR ESTABLISHING ANELECTRIC FIELD BETWEEN SAID ARRAY AND SAID ANODE; AND MEANS RESPONSIVEUPON CONNECTION OF THE ARRAY TO ANOTHER SOURCE OF ELECTRICAL ENERGY TOPROVIDE WITHIN THE ARRAY AND SUBSTANTIALLY THROUGHOUT THE SPACES BETWEENSAID WAFER-LIKE ELEMENTS ELECTRIC FIELDS SUPPLEMENTING SAIDFIRSTMENTIONED FIELD IN CONTROLLING THE MOVEMENT OF NEGATIVE CHARGEDPARTICLES ALONG SAID SPACES AND TOWARD SAID ANODE.